Research on human cytomegalovirus (CMV) is proposed to develop an understanding of herpes-like viruses with a restricted host range and a slow process of replication compared to that of herpes simplex virus. The problem is to be approached by characterizing CMV protein synthesis in permissive human fibroblast cells and nonpermissive cells of human or animal origin. In nonpermissive cells of animal origin, CMV induces the synthesis of virus-specific antigens and cytopathic effects are detectable but virus-DNA is not synthesized and infectious virus is not propagated. The conditions that render human lymphocytes permissive or nonpermissive for CMV replication will be studied. It is also proposed to examine the fate of parental CMV DNA in an attempt to explain the long delay prior to CMV macromolecular synthesis in infected cells. The rate of CMV protein synthesis, the fate of parental CMV DNA, and the effect of nonpermissive conditions for CMV replication will be relatd to the latent or persistent infectious potential of CMV in humans.